Although osteoporosis is more common in women, men also incur substantial bone loss with aging and approximately one-third of all hip fractures occur in men. In contrast to our understanding of the etiology and prevention of osteoporosis in women, considerably less is known about the determinants of skeletal health in men, especially among non-white men. We propose to address this gap in knowledge by continuing our Tobago Bone Health Study, a population-based study of BMD in 2,500 men aged 40-92 years at study entry who are primarily of African heritage (97 percent). All men who completed the baseline clinic exam will be recontacted for a second round of examinations as part of the current application, with an average follow-up of 4.5 years. Based on our past experience with this cohort, we expect that at least 75 percent of the surviving men will return for the second exam. BMD at the proximal femur will be remeasured using dual-energy x-ray absorptiometry (DXA), and the annualized rate of change in BMD determined. This second round of exams will also allow us to make new measures of trabecular and cortical volumetric BMD and bone structural geometry at both weight bearing and non-weight bearing skeletal sites using peripheral quantitative computed tomography. Previously collected data and stored blood and DNA specimens will be used to accomplish the following specific aims: (1) to describe the age-related patterns and rates of change in BMD among men of African descent; (2) identify the independent determinants oftrabecular and cortical volumetric BMD; (3) in a subset of the cohort, to determine the extent to which circulating sex steroids, calciotropic hormones and growth factors influence volumetric BMD, bone structural geometry and the rate of change in BMD with aging; and (4) to evaluate the association of volumetric BMD, bone structural geometry and rate of change in BMD with aging with variation in genes related to growth factor, calciotropic hormone, and cytokine structure and function. The proposed project will be the largest and most comprehensive evaluation of skeletal status in black men and will considerably advance our understanding of the determinants of bone health in men of African descent.